1. Field of the Invention
Liposomes can be formed from phospholipid molecules that are not very soluble in aqueous media but are soluble in organic solvents
A species of the field is the establishment of a liposomal delivery system that anchors aromatic hydrocarbon derivatives, such as mosquito repellents and insecticides, to the stratum corneum of a warm blooded host.
"Liposome" and "vesicle" may be used interchangeably herein because the art is not sufficiently exact with respect to the parameters of nomenclature.
2 Description of Prior Art
Liposomes are known to encapsulate water soluble pharmacological agents in their core volume. Thus, these agents are separated in minute particles from the surrounding media The liposomes have potential for site specific delivery, as known in the prior art, for their use as carriers to enhance therapeutic and protective indices.
The prior art method of making vesicles, or liposomes, is to subject a mixture of amphipatic phospholipid, such as egg lecithin, and an aqueous solution of the intended burden to high energy output, such- as sonication or microfluidization. The amphipatic lipid breaks into smaller units which form bladders known as vesicles or liposomes. In the process, some of the aqueous medium is captured in the core volume of the liposomes.
This basic known system, as described, is satisfactory for aqueous media but is inoperative for organic molecules that are minimally soluble in aqueous media.
This invention distinguishes over all known prior art, including intensive literature studies, by the discovery that formation of amphipatic lipids into vesicles in the presence of organic molecules that are minimally soluble in aqueous media exhibit a phenomenon of sequester by lamellar liposomal entrapment of the organic substance in the manner illustrated in the drawing. The organic substance would not ordinarily be expected to fill the aqueous core volume of a vesicle/liposome during formation. The outermost portion of a bipolar lipid membrane, both on the exterior surface and on the core volume wall, is a hydrophilic sphere. Therefore, it is generally accepted as fact that an organic substance would not be encapsulated.
It is an object of this invention to provide a slow release delivery system for chemicals which are soluble in an organic solvent, and not water soluble, by capture of such chemicals in a bipolar lipid vesicle. This object is carried out by lamellar envelopment.
Another object of the invention is to provide an anchor molecule for such sequestered agent, the anchor molecule being selected to have affinity for the desired host surface under consideration. The primary target surface of the preferred embodiment is the stratum corneum. Stratum corneum is defined in Tabor's Cyclopedic Medical Dictionary, Edition 14 (F. A. Davis Company) as the outermost horny layer of the epidermis.